[Ultrasound in the early diagnosis of congenital dislocation of the patella].

INTRODUCTION

Congenital dislocation of the patella is defined as lateral dislocation of the patella present at birth, impossibility of closed reduction and diagnosis before the age of 10 years. We report about a rare case of a bilateral congenital dislocation of the patella.

CASE REPORT: Physical examination of an eight-month- old boy showed bilateral knee flexion contractures associated with moderate genu varum. On both sides the patella could not be palpated easily. Radiographic diagnosis could not show the patella as the patella normally ossifies later. Ultrasound examination located the patella lateral to the lateral femoral condyle on both sides. Closed reduction was impossible. An open reduction with division of the lateral soft tissues, lateral release, and derotation of the quadriceps femoris and refining of the medial structures was performed. After cast removal the patellae were both located in the intercondylar grooves as confirmed by clinical and ultrasound examinations of both knees. Active and passive exercises were started.

CONCLUSION

Failure of internal rotation of the myotome which contains the quadriceps femoris and the patella is the etiology of congenital dislocation of the patella. The quadriceps acts as flexor, exerting a valgus stress on the knee, causing external rotation of the tibia. Diagnosis is often delayed because of the lack of pathological findings on plain radiographs. Early diagnosis is enabled by ultrasonography. Surgical treatment is necessary and results are good, as long as there are no secondary changes.